FIG. 1 shows an audio system of an aircraft according to the prior art. It comprises an audio management unit 10 to which are connected, on the one hand, pieces of audio equipment 121 to 12N (N=4 in this case) and, on the other hand, radiocommunications units 13, 14 and 15 in order to be able to communicate with stations on the ground by VHF, HF or by satellite (SATCOM) respectively. The pieces of audio equipment 12i (i=1 to N, N=4 in this case) comprise audio units 12ia for generating audio voice signals, the audio units being either a microphone 121a, or headsets 122a provided with microphones, for example for the pilots, the crew or mechanics on the ground, oxygen masks 123a, also provided with microphones, cabin handsets 124a, etc. These audio units are connected to the audio management unit 10 by cables 11. Each piece of audio equipment 12 is moreover equipped with a control unit 12b (121b to 12Nb, where N=4 in this case) generally appearing in the form of a press-to-talk button allowing an operator, such as a pilot, a co-pilot, a member of the cabin crew or a ground mechanic, to speak. Each control unit 12b is provided for generating a logic (on/off) control signal S which is conveyed, via a cable 16, to the audio management unit 10.
Thus, when an operator wishes to transmit a message by a piece of audio equipment 12, notably by his or her audio unit 12a, he operates the control unit 12b (if the control unit is a button, he presses the press to talk button 12b) of that piece of audio equipment 12. The logic control signal S generated by this operation is received by the audio management unit 10 and is retransmitted, via a selector 100, to the radiocommunications unit 13, 14 or 15 which has previously been selected by that operator, in connection with his audio equipment 12. On reception of the logic control signal S, the radiocommunications unit 13, 14 or 15 in question is activated and this happens as long as the logic control signal S is present, that is to say as long as the control unit 12b is being activated. The audio signals coming from the audio unit 12a of the audio equipment 12 are then conveyed via the management unit 10, in particular its selector 100, to the radiocommunications unit in question where they are transmitted by the latter.
FIG. 2 shows a timing diagram illustrating the operation of this audio system. The logic control signal S generated by the control unit 12b is at the 1 level when it is activated (the press to speak button is pressed) and at the 0 level in the opposite case. Also shown is the audio signal SA corresponding to the voice message that the operator sends whilst the radiocommunications unit is activated by the control signal S. This audio signal SA is transmitted from the audio unit 12a of the audio equipment 12 whose control unit 12b has be operated and directed to the radiocommunications unit previously selected in connection with that audio equipment 12.
The control unit 12b is generally a press-to-speak button also called “Push To Talk Switch” or “PTT Switch”.
An aircraft is generally equipped with six radiocommunications units for the voice function (2 HF, 3 VHF and 1 SATCOM), with seven pieces of audio equipment 12 and therefore with seven speech control units 12b each with their own cable 16.
The disadvantage of these audio systems is the large number of cables routed from the cockpit to the avionics bay in the hold, definitively two per cockpit audio equipment.
There are also other audio systems where the logic control signals are transmitted by sending data frames on a communications bus via a specific communications protocol.
The disadvantage of these audio systems is their relative complexity.
A purpose of the present disclosure is to provide an audio system that does not have the disadvantages mentioned above and therefore whose number of cables is low in comparison with the system of the prior art which is not of low complexity.
In order to do this, the present disclosure relates to an audio system for an aircraft which comprises:                a management unit to which are connected, on the one hand, by cables, pieces of audio equipment and, on the other hand, at least one radiocommunications unit,        each audio equipment comprising an audio unit for generating audio signals and a control unit.        
According to the present disclosure, it is characterized in that, on the one hand, each audio equipment comprises a generator which, under the control of the control unit, generates a pulsed coded audio signal and injects the signal into the same cable as that used for conveying the audio signals coming from the audio unit of the audio equipment, each code formed by a pulsed coded audio signal being representative of a piece of audio equipment, and in that, on the other hand, it comprises a decoder which, on reception of a coded audio signal generated by a piece of audio equipment, decodes it and generates a logic control signal in order to activate the radiocommunications unit which has previously been associated with the audio equipment represented by the code of the coded audio signal received and decoded.